The present invention generally relates to polyacrylate thickeners and to methods of making the thickeners. More particularly, the present invention is directed to a coating composition containing a polyacrylate thickener made from an ethyl acrylate monomer.
Broadly speaking, a thickener or thickening agent refers to an additive that is added to a composition in order to increase its viscosity or to otherwise alter its pour characteristics. One class of thickeners, polyacrylate thickeners, are used in a variety of different applications. For instance, polyacrylate thickeners have been found to be particularly well suited for use in adhesive coatings containing polymeric latex compositions. Such coatings are commonly used in the textile field.
For example, sodium polyacrylate is used as a thickener in carpet coatings of the type that are applied to the back of carpets for securing the carpet fibers to a base material. When used in these types of coatings, the sodium polyacrylate not only adjusts the viscosity of the coating to a desired level but also facilitates application of the coating to the textile product.
Currently, sodium polyacrylates are made by first polymerizing methyl acrylate to form a polymethylacrylate. The polymethylacrylate is then hydrolyzed using sodium hydroxide to produce a sodium polyacrylate. Unfortunately, during hydrolysis, methyl alcohol or methanol is also formed which remains in the thickener.
Methanol is flammable, poisonous, and is considered a hazardous substance. As such, methanol containing compositions are highly regulated and are subject to government reporting requirements. When using a methyl acrylate monomer to form a polyacrylate thickener, not only is the thickening agent subject to such government regulations but also any products or coatings that incorporate the thickener.
Further, when polyacrylate thickeners are incorporated into a textile coating and used, the coating is typically first whipped into a foam and then applied to a textile substrate. The methanol contained within the coating evaporates during application. Consequently, it is recommended that the coating only be applied in well ventilated areas and under careful monitored conditions.
Due to the above-concerns, a need exists for a polyacrylate thickener that does not contain substantial amounts of methanol and that is not considered hazardous or subject to governmental scrutiny. Also, a need exists for a polyacrylate thickener that does not release substantial amounts of methanol vapors during use.